I am learning F# syntax for my interview in a few days. I am not getting any syntax error highlights where I should be. Also, some lines of code works, other do not.

I am on:

1. VSCode Version 1.63.2 (Universal)
2. MacOs 12.2
3. Ionide-FSharp is installed
4. dotnet version 5.0.404

This works:

let mutable a = 10
a <- 20 //chaning a to 20
a //a is now 20

let items = [1..5] //creates list from 1 to 5
List.append items [6] //adds 6 to list of 6 --does not change 'items'

This does not work:

let prefix prefixStr baseStr = 
    prefixStr   ", "   baseStr

prefix "Hello" "World"

returns:

Microsoft (R) F# Interactive version 11.4.2.0 for F# 5.0
Copyright (c) Microsoft Corporation. All Rights Reserved.

For help type #help;;

> let prefix prefixStr baseStr = ;;

  let prefix prefixStr baseStr = ;;
  -------------------------------^^

/Users/MyName/Documents/learnf#/stdin(1,32): error FS0010: Incomplete structured construct at or before this point in binding
> # silentCd @"/Users/MyName/Documents/learnf#";;
- # 1 @"/Users/MyName/Documents/learnf#/001_fsharp_1.fs"
- ;;

CodePudding user response：

You're only sending the first line of your code to fsi.

Use your cursor to highlight all of this:

let prefix prefixStr baseStr = 
    prefixStr   ", "   baseStr

prefix "Hello" "World"

Then hit alt enter. It will send all 4 lines at once and give you what you want.

CodePudding user response：

If you're interested in finding bugs quickly and easily, use the official online compiler from fsharp.org.

• Lists in F# are immutable and any modifying operations generate new lists instead of modifying existing lists (FSharp.Core).

   let items = [1..5] //creates list from 1 to 5
   let items2 = List.append items [6]
  
   printfn "%A" items
   printfn "%A" items2
  
   -> [1; 2; 3; 4; 5]
   -> [1; 2; 3; 4; 5; 6]
  

• prefix "Hello" "World" The result of this expression is implicitly ignored. To discard this value explicitly use 'expr |> ignore', or bind the result to a name.

    let prefix prefixStr baseStr = 
    prefixStr   ", "   baseStr
  
    let text = prefix "Hello" "World"
  
    printfn "%s" text
  
    -> Hello, World